Detector and modulator circuits for passive microwave links

Abstract

An RF apparatus (e.g., a wireless label) provides improved backscattering of an incident RF signal by utilizing a separate modulator diode, which connects across the antenna, to modulate the backscattering of the antenna. A separate detector diode connects across the antenna through an impedance matching network to detect modulated signals received by the antenna.

The invention claimed is: 
     
       1. An RF apparatus, comprising an antenna,   a detector diode connected across the antenna to detect modulated signals received by the antenna, said detector diode connecting to the antenna through a matching network such that an impedance of the detector diode at a predetermined RF frequency conjugately matches an antenna port impedance transformed through the matching network, and   a modulator diode connected across the antenna to modulate backscattering of the antenna.   
     
     
       2. The apparatus of claim 1 wherein the antenna is a folded monopole. 
     
     
       3. The apparatus of claim 1 wherein the antenna is a dipole. 
     
     
       4. The apparatus of claim 3 wherein the dipole antenna is a half-wavelength long and the antenna port impedance is real. 
     
     
       5. The apparatus of claim 1 wherein the modulator diode is a tunnel diode. 
     
     
       6. The apparatus of claim 5 wherein the tunnel diode is biased off during the time when the apparatus is in a receiving mode. 
     
     
       7. The apparatus of claim 5 wherein the tunnel diode is biased in a negative resistance portion of its forward-biased region during the time when the apparatus is in a backscatter mode. 
     
     
       8. The apparatus of claim 5 wherein the tunnel diode is biased substantially at a valley voltage of its forward-biased region during the time when the apparatus is in the receiving mode. 
     
     
       9. The apparatus of claim 1 wherein the detector and modulator diodes connect across the antenna in different directions.   
     
     
       10. The apparatus of claim 1 wherein a detector circuit connects across the detector diode through a transmission circuit which provides an essentially open circuit impedance across the detector diode at the predetermined frequency.   
     
     
       11. The apparatus of claim 10 wherein the transmission circuit includes a quarter-wavelength transmission line connected between the detector diode and a capacitor at an input of a connected detector circuit. 
     
     
       12. The apparatus of claim 1 wherein a modulator circuit connects across the modulator diode through a transmission circuit including a quarter-wavelength transmission line connected across the modulator diode and a capacitor at an input of a connected modulation circuit. 
     
     
       13. The apparatus of claim 1 wherein the detector diode is a Schottky detector diode. 
     
     
       14. An RF apparatus for operating in at least a receiving mode and a backscattering mode, the apparatus comprising: an antenna for receiving an RF signal, the antenna having an antenna port impedance;   a detector circuit for detecting the RF signal during the receiving mode of the apparatus, the detector circuit comprising, a matching network, and   a detector diode connected across the antenna through the matching network such that an impedance of the detector diode at a predetermined RF frequency conjugately matches the antenna port impedance transformed through the matching network; and     a modulator circuit for modulating the signal for backscattering during the backscattering mode, the modulator circuit comprising, a modulator diode connected across the antenna to enhance the backscattering of the antenna, and   a baseband modulator circuit for activating and deactivating the modulator diode to modulate backscattering of the antenna.